1. Field of the Invention
The present invention relates to variable displacement compressors and particularly to compressors capable of sufficiently returning the lubricant oil to lubricate the mechanical parts of the compressor.
2. Description of the Related Art
As one type of known compressors, a variable displacement compressor is disclosed in U.S. Pat. No. 6,010,312 and includes pistons and a swash plate. Each piston is reciprocally inserted within a compressor cylinder bore and an end portion of each piston is coupled to a peripheral portion of the swash plate. The swash plate is inclinably coupled to a drive shaft in a crank chamber. The swash plate rotates together with the drive shaft. The compressor output discharge capacity can be changed by changing the piston stroke. The piston stroke can be changed in relation to an inclination angle of the swash plate. The inclination angle of the swash plate can change by changing the pressure within the crank chamber. When the pressure within the crank chamber increases, the inclination angle of the swash plate with respect to a plane perpendicular to the axis of the drive shaft decreases. As the result, the piston stroke decreases and the compressor output discharge capacity decreases. To the contrary, when the pressure within the crank chamber decreases, the inclination angle of the swash plate increases. As a result, the piston stroke increases and the compressor output discharge capacity increases.
The crank chamber is connected to a discharge chamber by a control passage. A control valve is provided within the control passage. When the control valve opens the control passage, high-pressure refrigerant within the discharge chamber is released into the crank chamber through the control passage and the pressure within the crank chamber increases. By increasing the pressure in the crank chamber, the inclination angle of the swash plate with respect to the plane perpendicular to the drive shaft axis decreases, the piston stroke decreases and the compressor output discharge capacity decreases.
In addition, mechanical elements in the compressor, such as bearings for the drive shaft, are necessarily lubricated by utilizing lubricant oil. Within the compressor, the oil mixes with the refrigerant and the oil is drawn and compressed together with the refrigerant. In the discharge chamber, the oil is separated by utilizing an oil separator and is delivered to the mechanical elements of the compressor. The separated oil is returned to the crank chamber through the control passage to lubricate mechanical elements in the crank chamber. However, the control valve closes the control passage during the operation of the compressor at its maximum capacity. As the result, the crank chamber can not be sufficiently lubricated when the compressor is operated continuously at the maximum capacity because the control valve closes the control passage to maintain the crank chamber in a low-pressure state and to provide the maximum output discharge capacity.
It is, therefore, an object of the present invention to provide a compressor that can reliably and constantly supply lubricant oil to the crank chamber.
Preferably, a variable displacement compressor includes a driving unit. The driving unit is provided within a compressor crank chamber and the compressor output discharge capacity decreases when the pressure within the crank chamber increases. Further, the compressor includes a control passage, a control valve and a throttle passage. The control passage releases the refrigerant from the discharge pressure area into the crank chamber. The control valve is provided within the control passage and opens or closes the control passage. When the control valve opens the control passage, the refrigerant is released from the discharge port to the crank chamber to increase the pressure within the crank chamber, thereby decreasing the compressor output discharge capacity.
The throttle passage delivers oil within the compressed refrigerant to the crank chamber regardless of whether the control valve has opened or closed the control passage. Because the throttle passage continuously delivers oil to the crank chamber, even when the control passage has been closed by the control valve, the moving mechanical elements within the crank chamber can be reliably and sufficiently lubricated and the crank chamber is prevented from being insufficiently lubricated.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.